1. Field of the Invention
The present invention relates, in general, to electric watthour meters and, more specifically, to test devices for installing watthour meters.
2. Description of the Art
Electric watthour meters are commonly used to measure electric power consumption at a building, home or other site. Typically, a meter socket is attached to an exterior wall surface of the building or home. The socket includes, for single phase electrical service, a pair of line terminals and a corresponding pair of load terminals. The incoming electrical power conductors are connected to the line terminals. The building electrical wiring circuits are connected to the load terminals, typically through an intermediate service panel mounted within the building or home which contains at least one main circuit breaker and a number of individual circuit breakers or fuses for each electrical circuit.
In a conventional socket-type meter application, the meter socket includes jaw-type line and load terminals which receive corresponding blade terminals extending outward from the base of a watthour meter in a push-in connection.
However, it is potentially dangerous for a watthour meter installer to mount the watthour meter in a socket if the watthour meter socket is not properly wired, or if a short circuit, improper ground or a backfeed condition exists. As a result, a single-phase meter socket tester, type S-120, was devised by Ekstrom Industries, Inc., Farmington Hills, Michigan. This meter socket tester has found widespread application in the electric utility industry.
As shown in FIGS. 1 and 2, the S-120 meter socket tester includes a base having at least four blade-type terminals extending outward therefrom for insertion into the jaw terminals of a meter socket. A clear plastic cover is mounted on the front surface of the base and covers the interior circuitry mounted on the base which includes four blade terminals arranged in spaced pairs as line and load terminals, a pair of fuses, and two pairs of lights, referred to as "safe lights" and "fault lights". A spare set of fuses are also mounted within the cover on the front surface of the base. A handle is attached to the cover and provides an easy means for inserting and removing the meter socket tester to and from a watthour meter socket.
As shown in FIG. 2, the circuitry of the S-120 meter socket tester connects the pair of safe lights in series with accompanying resistors between the load terminals. A fault light is connected in parallel with each fuse between one line terminal and one load terminal.
In use, the installer places the S-120 meter socket tester into the socket such that the bottom two load blade terminals of the tester touch the bottom two jaw or load terminals of the meter socket. If both safe lights glow, indicating a backfeed condition, internal jumpers in the socket, or a reversal of line and load wiring, the installer is made aware that a fault exists and that corrective action is necessary. The installer, assuming that one or both of the safe lights did not glow in the initial step, will then insert all of the terminals of the socket tester into the jaw terminals in the meter socket. If both safe lights glow, there is no fault present and the installer can safely install the watthour meter in the socket. However, if only one safe light or any fault lights glow, the installer must then determine the nature of the fault and correct it, disassemble the handle and cover, refuse the socket tester, reassemble the handle and cover, and repeat the above-described testing procedure. The fault lamps will glow whenever the associated fuse blows. This can occur when the customer's main disconnect switch is closed and a load of more than 30 amps is present. A properly wired meter socket is indicated by both safe lights glowing and no fault light glowing when the socket tester is fully inserted into the meter socket terminals.
While the above-described S-120 meter socket tester has been found to be effective in detecting watthour meter socket wiring errors or fault conditions prior to the insertion of a watthour meter into the socket, the testing procedure using the S-120 meter socket tester is difficult and requires a number of individual steps to determine the nature of the fault. Further, there is no indication that the safe or fault lights are still operative and, if any of such lights are inoperative, the meter socket tester becomes wholly or partially inoperative.
A further problem existing with the use of the above-described S-120 meter socket tester is that the use of the socket tester and the installation of the watthour meter into the meter socket should be done only if the customer's main circuit disconnect switch is open. If this is not done, it is possible to blow the fuses in the socket tester and cause the fault lights to glow indicating an energize load of 30 amps or more. However, it is common for the building to which the meter is to be installed to be locked thereby preventing access to the internal main circuit disconnect switch. Thus, the installer has no means to indicate that a circuit within the building is active when the meter is installed. Depending upon the nature of such circuit, the circuit load could be connected up to 30 amps if the meter is installed. This could result in a dangerous condition if the circuit includes, for example, an electric stove or heater having combustible materials present on or in proximity to the burners thereof.
Thus, it would be desirable to provide an improved watthour socket tester which overcomes the problems of previously devised watthour socket testers. It would also be desirable to provide a watthour meter socket tester which easily and safely determines the wiring connections of a meter socket prior to the installation of a watthour meter therein. It would also be desirable to provide a watthour meter socket tester which provides an indication of any load current prior to the installation of the watthour meter. It would be desirable to provide a watthour meter socket tester which includes means for testing the fault lamps for proper operation. Finally, it would be desirable to provide a watthour meter socket tester which provides access to the fuses without removing the handle and cover from the tester or exposing the installer to the energized circuit in the tester.